1. Field of the Invention
The present invention relates in general to superchargers for automotive internal combustion engines or the like and more particularly to a bearing holding arrangement in a supercharger.
2. Description of the Prior Art
An example of a bearing holding arrangement in a supercharger is disclosed in Japanese Provisional Utility Model Publication No. 61-134536 and also shown in FIG. 9.
Referring to FIG. 9, the bearing holding arrangement includes a pair of oil film dampers 10, 12 installed, by way of oil films, on an inner circumferential wall 14a of a bearing housing 14 and a pair of ball bearings 16, 18 the outer rings of which are respectively installed on the oil film dampers 10, 12. The inner rings of the ball bearings 16, 18 are installed on a turbine shaft or rotor shaft 20 and stationarily held thereon. The oil film dampers 10, 12 are axially urged away from each other by a coil spring 22 so that the outer rings of the ball bearings 16, 18 are resiliently held in place relative to the inner rings. A pair of stopper rings 24, 24 are installed on the inner circumferential wall 14a of the bearing housing 14 so that the oil film dampers 10, 12 selectively abut upon the stopper rings 24, 24 to hold the ball bearings 16, 18 and therefore the rotor shaft 20 axially in place relative to the bearing housing 14.
In use, lubricating oil is supplied from an oil supply port 26 to annular chambers 28, 30 and then through passages 10a, 12a to the ball bearings 16, 18 to lubricate and cool the same and at the same time supplied to annular spaces 32, 34 between the dampers 10, 12 and the inner circumferential wall 14a of the bearing housing 14 to form thereat oil films. The ball bearings 16, 18 are thus installed in a floating state within the bearing housing 14 and therefore vibrations of the rotor shaft 20 are absorbed by the oil films for thereby eliminating or at least reducing the otherwise occuring noise and improving the durabilities of the rotor shaft 20 and ball bearings 16, 18.
With such a prior art bearing holding arrangement, the stopper rings 24, 24 are expected to hold or locate the rotor shaft 20 axially in place relative to the bearing housing 14. In this connection, if the locational accuracy by the stopper rings 24, 24 is low, the clearances between the turbine wheel and compressor wheel and their associated inner walls of turbine and compressor housings cannot be maintained at suitable values, thus deteriorating the operational efficiency of the supercharger. Accordingly, the locational accurancy by the stopper rings 24, 24 needs to be maintained high.
However, with the prior art stopper ring arrangement, it is quite difficult to maintain the locational accuracy high. That is, as shown in FIG. 10, in order that the stopper rings 24, 24 can assuredly and easily fit in grooves 14b, 14b formed in the inner circumferential wall 14a of the bearing housing 14, it is necessary for each groove 14b to have an axial clearance "C". When the clearance "C" is small, the efficiency of the work for installation of the stopper rings 24, 24 is considerably lowered. When the clearance "C" is large, the positions of the stopper rings 24, 24 vary largely within the limit of the clearance "C", thus causing a problem that it is impossible for the stopper rings 24, 24 to locate or hold the oil film dampers 10, 12, the ball bearings 16, 18 and therefore the rotor shaft 20 accurately in place.